Contribution to authorship
YQY and CX screened abstracts, selected eligible papers, extracted data
and wrote the first draft of the paper. SSH and MYS screened abstracts
and selected eligible papers. HHL, LYH and QW performed the statistical
analysis. CLW, YW, LX and XFL helped in the final selection of papers in
case of disagreement and reviewed the manuscript critically. JHT, LG and
LS designed the study and revised the manuscript.